Shaft member for fluid lubrication bearing apparatuses and a method for producing the same

ABSTRACT

A low-cost shaft member for hydrodynamic bearing apparatuses restores the pressure balance in a thrust bearing gap formed on both axial sides of the flange portion in an early stage. A shaft material integrally having a shaft portion and a flange portion with a through-hole between both end faces of the flange portion is formed in a common forging step. As a result, the through-hole is formed to open to an inner diameter side of the bearing gaps avoiding the thrust bearing gaps formed on both end faces of the flange portion of the shaft member as a finished product.

This application is a divisional of Ser. No. 11/630,410 filed on Jun.13, 2007, now abandoned which is a National Stage Application ofInternational Application Serial No. PCT/JP2005/016399, filed Sep. 7,2005.

BACKGROUND OF THE INVENTION

The present invention relates to a shaft member for fluid lubricationbearing apparatuses which relatively rotatably supports a shaft memberin the radial direction by a lubricating film of a fluid which occurs ina radial bearing gap and a method for producing the same.

Fluid lubrication bearings of this type are roughly classified into twogroups: a hydrodynamic bearing comprising a hydrodynamic pressureproducing means for producing hydrodynamic pressure in a lubricating oilin a bearing gap; and so-called cylindrical bearings (bearingscomprising a perfectly circular bearing face) not comprising ahydrodynamic pressure producing means.

For example, a fluid lubrication bearing apparatus incorporated in aspindle motor of a disk drive unit such as HDD is provided with a radialbearing portion which rotatably supports a shaft member in the radialdirection in a non-contact manner; and a thrust bearing portion whichrotatably supports the shaft member in the thrust direction in anon-contact manner. a bearing (hydrodynamic bearing) which is providedwith grooves for producing a hydrodynamic pressure (hydrodynamic groove)on the inner periphery face of a bearing sleeve or on the outercircumferential surface of the shaft member is used as a radial bearingportion. As a thrust bearing portion, for example, both end faces of theflange portion of the shaft member or a hydrodynamic bearing providedwith hydrodynamic grooves on the face facing it (an end face of thebearing sleeve, an end face of a bottom member fixed on a housing, theinner bottom face of the bottom of the housing or the like) is used (forexample, refer to patent document 1: Japanese Unexamined PatentPublication No. 2002-61641). Alternatively, as the thrust bearingportion, a bearing having the structure in which one end face of theshaft member is supported in a contact manner by a bottom member(so-called pivot bearing) is used in some cases (for example, refer topatent document 2: Japanese Unexamined Patent Publication No.1999-191943).

In a spindle motor of this type, a clamper for clamping a disk-shapedinformation recording medium such as magnetic disks (hereinafterreferred to simply as a disk) between a disk hub and itself is attachedto the edge of the shaft member. The clamper is attached on the shaftmember by screwing into a threaded hole formed on one edge of the shaftmember through the clamper (for example, refer to patent document 3:Japanese Unexamined Patent Publication No. 2000-235766).

Recently, to deal with increased information recording density andhigher rotational speed in information appliances, higher rotationalaccuracy is required for the above spindle motor for informationappliances. To meet this demand, higher rotational accuracy is alsorequired for a fluid lubrication bearing apparatus incorporated into theabove spindle motor. At the same time, with the demand for lower priceof information appliances, reduced production costs of the above fluidlubrication bearing apparatus are strongly desired recently.

In order to stably provide the rotational performance of a fluidlubrication bearing apparatus (hydrodynamic bearing apparatus) for thelong term, it is important to control the radial bearing gap and thrustbearing gap, in which the pressure of the fluid for supporting the shaftmember is present, to be highly accurate. For example, when the thrustbearing gap is formed on both side of the flange portion in the axialdirection as mentioned above, to maintain the thrust support of theshaft member in a stable state, the pressure for the thrust support onone end face side of the flange portion and the pressure for thrustsupport on the other end face side need to be brought into balance sothat the sliding contact of the end face of the flange portion and theface facing it is avoided as much as possible. Higher accuracy of thethrust bearing gap can be achieved by processing the end face of theflange portion facing this, hydrodynamic grooves and the like highlyaccurately, but merely increasing processing accuracy willinappropriately result in higher costs.

Moreover, examples of methods for forming a threaded hole on the shaftmember include a method comprising forming a prepared hole of thethreaded hole on the shaft material by cutting, and a thread cutting isworked relative to this prepared hole. However, by this method, cuttingpowders produced when the prepared hole is cut are accumulated at thebottom of the threaded hole, and cutting powders cannot be completelyremoved even if the threaded hole is cleaned after the process.Accordingly, the cutting powders remaining inside the threaded holedeposit to other components as contaminants when other components aremounted or a bearing apparatus is assembled, and may get in the fluid(for example, lubricating oil, etc.) filling the inside of the bearingapparatus after being assembled. Alternatively, if the cutting powdersdeposited to other components (contamination) are further transferred todisks, they may cause disk crash. Moreover, removal of cutting powdersrequires complicated and numerous cleaning steps, leading to an increasein costs.

Moreover, to deal with cost reduction required for the above fluidlubrication bearing apparatus, various cost reducing measures areexamined for the component parts of fluid lubrication bearingapparatuses. For example, as for the shaft member, an article comprisingthe shaft portion and the flange portion integrally formed by forging toproduce a near net shape is known (for example, refer to patent document4: Japanese Unexamined Patent Publication No. 2004-347126).

BRIEF SUMMARY OF THE INVENTION

On one hand, forging is a method having excellent processability andcost performance as mentioned above, but on the other hand, due to itscharacteristics, required dimensional accuracy may not be obtaineddepending on the shape of the shaft member.

More specifically, the forging process includes compressing a materialto deform it in a specific direction into a predetermined shape. Forexample, when the pressing direction in forging is the same as thelongitudinal direction of the material, compressive force imparted toone end of the material is not sufficiently transmitted to the otherend, and thus plastic flow at the other end may be renderedinsufficient. This prevents the deformation enough to attain a desiredshape, preventing to obtain high forming accuracy.

In particular, with recent demand for increased capacity diskapparatuses, a fluid lubrication bearing apparatus (hydrodynamic bearingapparatus) which can load a plurality of disks and is integrated in aspindle motor, the use of an elongated shaft member compared to thoseknown is examined to cope with an increase in moment load. However, itselongation tends to cause problems in the plastic flow abobe mentionedmore evidently. Therefore, it is difficult to produce a shaft memberhaving both elongated length and high dimensional accuracy at low costsat the moment.

A first object of the present invention is to provide a shaft member forhydrodynamic bearing apparatuses which can restore the pressure balancein a thrust bearing gap formed on both side of a flange portion in theaxial direction in an early stage at low costs.

A second object of the present invention is to provide a shaft memberfor fluid lubrication bearing apparatuses which can prevent contaminantsfrom depositing to bearing component parts and prevent contaminants fromgetting inside a bearing apparatus as much as possible at low costs.

A third object of the present invention is to provide a shaft member forfluid lubrication bearing apparatuses which has high dimensionalaccuracy and can be elongated at low costs.

To achieve the first object, the present invention provides a shaftmember for hydrodynamic bearing apparatuses, the shaft member comprisinga flange portion and being supported in a non-contact manner in thethrust direction by the pressure produced by hydrodynamic effect of afluid which occurs in a thrust bearing gap on both axial sides of theflange portion, a through-hole opening to its both end faces beingformed on the flange portion, and the inner periphery of thethrough-hole being processed by plastic processing.

In the present invention, as stated above, a through-hole opening to itsboth end faces is formed on the flange portion. Hence, when the fluidpressure in the thrust bearing gap on an axial end side is extremelyincreased for any reason, the fluid (for example, lubricating oil) flowsinto the thrust bearing gap on the other axial end side via thethrough-hole formed on the flange portion. Accordingly, pressure balancein both thrust bearing gaps is restored at an early stage to maintainthe width of the thrust bearing gaps appropriately, and the slidingfriction between the end face of the flange portion and the face facingit can be prevented beforehand.

An example of the methods of forming the through-hole on the flangeportion includes cutting. However, cutting suffers a long cycle time,whereby processing efficiency is lowered and costs are increased.Moreover, cutting inevitably produces cutting powders, which may get inthe fluid as contaminants. In order to prevent this contamination, acleaning process of the shaft member needs to be additionally performedafter cutting, resulting in increased costs. In particular, as thediameter of the flange portion is several millimeters in the abovehydrodynamic bearing apparatus used in information appliances, thediameter of the through-hole will be as minute as several tens toseveral hundreds micrometers accordingly. In this case, it is difficultto completely remove cutting powders after cutting, and therefore acareful cleaning step or other process is necessary, which inevitablyraises the costs.

In contrast, plastic processing typically including forging have ashorter cycle time compared to cutting in general, and can process veryefficiently. Moreover, since cutting powders are not produced unlike incutting, the cleaning step is unnecessary. Therefore, forming thethrough-hole by plastic processing can greatly reduce the costs. In thiscase, the inner periphery of the through-hole will be a face subjectedto plastic processing. As a face subjected to plastic processing has alow level of roughness, smooth flow of the fluid in the through-holewithout performing a special post-treatment can be ensured.

The through-hole is desirably formed in the vicinity of the shaftportion. By forming the through-hole in the vicinity of the shaftportion, the passage of the fluid between the two thrust bearing gaps isalso ensured on the inner diameter side of the flange portion. Theregulating function of the pressure balance between the two thrustbearing gaps can be increased, as well as the fluid passage (an annulargap between the outer circumferential surface of the flange portion andthe inner periphery face of the housing) on the outer diameter side ofthe flange portion which is originally there. From this perspective, thethrough-hole desirably opens to the inner diameter side of the radialcenter of the thrust bearing gap. In this case, the through-hole isdesirably disposed so that it opens at a position avoiding the thrustbearing gap between the region in which the hydrodynamic grooves areformed and the face facing it (the inner diameter side of the thrustbearing gap) to prevent the so-called drop of the hydrodynamic pressure(loss of the hydrodynamic pressure). If it is difficult to make thethrough-hole open to said position due to a spatial limit or any otherfactor, it may open to a position overlapping the thrust bearing gap.However, it is desirable to avoid, if possible, a drop in thehydrodynamic pressure also in this case.

The above shaft member for hydrodynamic bearing apparatuses, forexample, can be provided as a hydrodynamic bearing apparatus comprisinga shaft member; a bearing sleeve into which this shaft member isinserted at its inner periphery; a radial bearing portion which producespressure by the hydrodynamic effect of a fluid which occurs in a radialbearing gap between the outer periphery of the shaft portion and theinner periphery of the bearing sleeve to support the shaft portion inthe radial direction in a non-contact manner; a first thrust bearingportion which produces pressure by the hydrodynamic effect of a fluidwhich occurs in a thrust bearing gap on one end side of the flangeportion to support the flange portion in the thrust direction in anon-contact manner; and a second thrust bearing portion which producespressure by the hydrodynamic effect of the fluid occurring in the thrustbearing gap on the other end side of the flange portion to support theflange portion in the thrust direction in a non-contact manner.

The fluid is caused to flow in the axial direction in the radial bearinggap by forming hydrodynamic grooves asymmetrically in the axialdirection for producing the hydrodynamic effect of the fluid on one ofthe outer circumferential surface of the shaft portion facing the radialbearing gap and the inner periphery face of the bearing sleeve opposingthis outer circumferential surface. If this flow is directed to theflange portion, the occurrence of negative pressure in the bearingapparatus can be avoided, and the function of the through-hole toregulate the pressure balance equilibrates high pressure caused bypushing to the flange portion.

The above hydrodynamic bearing apparatus can be also presented as amotor which comprises a hydrodynamic bearing apparatus, rotor magnet andstator coil.

Moreover, to achieve the first object, the present invention provides amethod for producing a shaft member for hydrodynamic bearing apparatuseswhich comprises a shaft portion and a flange portion and is supported inthe thrust direction in a non-contact manner by the hydrodynamic effectof a fluid which occurs in the thrust bearing gap on both axial sides ofthe flange portion. The method comprises integrally forming the shaftportion and the flange portion by forging and forming a through-holeopening to both of the end faces of the flange portion by forging, theforging being performed simultaneously. As mentioned above, the formingof the through-hole is performed by a forging process so that cuttingpowders and the like associated with the cutting process can beprevented, and a cleaning step after the cutting process can be omittedor simplified. Moreover, the forming of the through-hole and the formingof the shaft material comprising the shaft portion and the flangeportion integrally are both performed simultaneously by forging, wherebythe processing steps can be simplified and the time for the process canbe greatly shortened.

To achieve the second object, the present invention provides a metallicshaft member for fluid lubrication bearing apparatuses in which athreaded hole is formed on its one end and a radial bearing face facingthe radial bearing gap is formed on the outer periphery, the threadedhole being formed by plastic processing. Herein, the radial bearing facemay be any that faces the radial bearing gap which produces ahydrodynamic effect, regardless of whether or not the hydrodynamicgrooves for producing the hydrodynamic effect are formed.

As mentioned above, the threaded hole is formed by plastic processing inthe present invention. Therefore, cutting needs not be performed to formthe threaded hole, cutting powders produced by cutting can be prevented.Accordingly, cutting powders do not remain inside the threaded hole.Furthermore, cutting powders can be prevented from depositing to othercomponents as contaminants when other components are mounted or abearing apparatus is assembled and from getting in a lubricating oil orthe like filling the inside of the bearing apparatus after beingassembled. Moreover, unlike in cutting, since cutting powders are notproduced in a large amount, the cleaning step can be simplified andrelated forming costs can be reduced.

The threaded hole can be, for example, so constructed that it has aprepared hole formed by a forging process and a thread portion formed byrolling process on the opening side of the prepared hole. In this case,as plastic processing, a forging process is performed on the preparedhole, and a rolling process is performed on the thread portion. Theprepared hole by the forging process is formed in a series from theshaft ends. After this prepared hole is formed, the opening side of theprepared hole is partially subjected to screw rolling so that the finalthreaded hole is constituted by the thread portion on the opening sideand the unrolled prepared hole remaining on the bottom side of the hole.Because this threaded hole is formed only by plastic processing,production of cutting powders can be prevented and the problem ofcontamination can be solved. Moreover, a shaft material having a shapecorresponding to the shaft member, for example, the shaft material whichintegrally has the shaft portion and flange portion can be formed byforging.

Moreover, since the above threaded hole is for fixing other componentson the shaft member, the accuracy of the perpendicularity of the shaftmember and other components screw-fixed on the shaft member variesdepending on how the threaded hole is inclined relative to the shaftmember. An example of the methods for suppressing the inclination of thethreaded hole relative to the shaft member is increasing the processingaccuracy of the prepared hole which serves as the reference inprocessing the thread portion of the threaded hole. When the preparedhole is formed by a forging process as in the present invention, themethod by which a pin for forming the prepared hole is pushed into theshaft material to cause the pushing portion to undergo plasticdeformation is employed. However, if an edge is formed between a conicalend face of the pin tip and a cylindrical outer circumferential surfacepositioned on its proximal end side (connecting portion), when the pinis pushed, a great amount of stress is concentrated at a portioncorresponding to the edge of the shaft material (for example, a portionwhich is deformed in conformity with the edge formed at the connectingportion between the pin tip face and the outer circumferential surfaceof the shaft material). If a raw material forming the shaft material is,for example, stainless steel or like material with poor ductility, thistrend becomes more evident. In its worst case, cracks are formed at theportion where stress is concentrated. In consideration of this problem,the prepared hole of the threaded hole is shaped so that it has aconical surface and a cylinder face which is disposed on the openingside of this conical surface and is smoothly continuous with the conicalsurface via a radially curved surface in the present invention.

Since the shape of the prepared hole is correspondent to the shapedeformed in conformity with the surface shape of the pin for forming theprepared hole, such a constitution means that the tip portion of the pinis in a conical surface shape, and that the conical surface of the tipportion of the pin is smoothly continuous with the cylindrical outercircumferential surface via the radially curved surface. Therefore, whenthe pin having the above-mentioned shape is pushed into the shaftmaterial, a portion corresponding to the connecting portion between thepin tip face of the shaft material and the outer circumferential surfaceof the cylinder is deformed in conformity with the smooth connectingportion of the pin, and the concentrated stress at the portioncorresponding to this connecting portion is mitigated. This can increasethe yield rate of products in forming of the prepared hole, ensuring theformation of the prepared hole. Moreover, since the pushing direction ofthe pin is stabilized by forming the tip of the pin in a conical shape,runout of the tip can be prevented for accurate pushing of the pin intothe shaft material, the dimensional accuracy of the prepared hole, inparticular the inclination of the axis of the prepared hole relative tothe axis of the shaft member can be suppressed to a low level.

Examples of more preferable shapes of the prepared hole include such ashape that the top of the conical surface formed at the bottom of theprepared hole is removed. The shape of a pin forming the material to beprocessed into this shape may be in such a shape that the tip portion ofthe pin in the form of a sharp cone is removed (for example, radiallycurved surface or a flat face). Accordingly, when the prepared hole isformed, not only at the portion corresponding to the connecting portionbetween the pin tip face of the shaft material and the outercircumferential surface of the cylinder, but also the stressconcentrated at a portion corresponding to the pin tip face top can bemitigated, further ensuring forming of the prepared hole.

Moreover, when the shaft member is in rotation, high perpendicularityrelative to the shaft member for a component is required fixed on theshaft member of the fluid lubrication bearing apparatus to avoid contactwith components on the fixed side of the bearing apparatus, runout orprevent other problems. Accordingly, in the present invention, thecoaxiality of the center line of the pitch circle of the thread portionin the threaded hole formed on the shaft member is set to 0.2 mm orlower. Herein, the coaxiality refers to the dimension of the deviationfrom the datum axis straight line of an axis (referring to the centerline of the pitch circle of the thread portion herein) which is to be onthe same straight line as the datum axis straight line (theoreticallycorrect axis line as a geometric reference. Moreover, the term axis lineused herein refers to an axis which is a geometrically correct straightline of the shaft member), and its dimension is represented by thediameter of the smallest geometrically correct cylinder which includesthe entire above axis (pitch circle center line) and is coaxial with thedatum axis straight line.

Accordingly, for example, the clamper for clamping the disk between thedisk hub and itself is screw fixed on the shaft member with its clampingface perpendicularly intersecting the axis of the shaft member, the diskis fixed with its disk plane remaining parallel to the clamper and theclamping face of the disk hub. Accordingly, the disk can be fixed whilethe value of the perpendicularity relative to the shaft member issuppressed to a low level, and runout of the disk relative to the shaftmember when the shaft member is in rotation can be suppressed.

Moreover, to achieve the second object, the present invention provides amethod for producing a shaft member for fluid lubrication bearingapparatuses, the shaft member comprising a threaded hole formed on itsone end and a radial bearing face facing a radial bearing gap formed onits outer periphery, the method comprising forming a prepared hole ofthe threaded hole by forging on a metallic shaft material, and thenforming a thread portion in the prepared hole by rolling to form thethreaded hole.

According to such a producing method, since forming of the threaded holedoes not require cutting, cutting powders produced by cutting can beprevented. The cutting powders thus do not remain inside the threadedhole. In addition, the cutting powders are prevented from beingdeposited to other components as contaminants when other components aremounted or a bearing apparatus is assembled, causing disk crash orgetting in a lubricating oil or the like filling the inside of thebearing apparatus after being assembled. Moreover, as mentioned above,instead of cutting, a forging process or a rolling process can be alsoused to shorten the cycle time and reduce material costs with animproved ratio of the amount of the material prior to the formingprocess to that after the process.

Moreover, the shaft material and the prepared hole can be formed in acommon forging step. According to this method, because forming of theprepared hole and forming of the shaft material are performed both byforging, such a process can be performed at a time so that the formingstep can be simplified.

The above shaft member for fluid lubrication bearing apparatuses can beprovided as a fluid lubrication bearing apparatus comprising, forexample, a shaft member for fluid lubrication bearing apparatuses; and asleeve member into which this shaft member is inserted at its innerperiphery and which forms the radial bearing gap between itself and theshaft member, the apparatus retaining the shaft member and sleeve memberin a non-contact manner by a lubricating film of a fluid produced in theradial bearing gap.

Moreover, the above fluid lubrication bearing apparatus can be providedas a motor comprising this fluid lubrication bearing apparatus, a rotormagnet and a stator coil.

To achieve said third object, the present invention provides a metallicshaft member for fluid lubrication bearing apparatuses which comprises ashaft portion and a flange portion, at least the shaft portion beingformed by forging, the shaft portion having a recess formed on its tipface, and the recess comprising a plastically processed surface.

Examples of means for achieving said object include a method ofincreasing the pressing pressure in forging. However, simply increasingpressing pressure may cause increased strain in the mold and rawmaterials, reduced mold life, cracks in raw materials, and various otherproblems. In contrast, in the present invention, since a concavecomprising a plastically processed surface on the tip face of the shaftportion is formed, that is, the concave is formed by the plasticdeformation of the tip portion of the shaft portion, the material whichwas originally in the concave is pushed out to the outer diameter sideand the tip side by forming of the concave. Accordingly, the tip portioncan be formed by minimizing the occurrence of shortage of thedeformation amount at the tip portion by performing the forging processof the shaft portion and plastic processing of the concave. Therefore,when the shaft member is elongated, the deformation amount at the tipportion of the shaft portion can be ensured and high forming accuracycan be obtained throughout the length of the shaft portion. In addition,as mentioned above, since forming accuracy can be increased withoutincreasing the pressing pressure, it is economical that no concern aboutreduced mold life, etc., is necessary.

A preferred concave formed on the tip face of the shaft portion, forexample, has a shape whose diameter gradually decreases from the tip ofthe shaft portion toward the center of the shaft portion. Thisconstitution has been created based on the tendency that its deformationshortage grows larger as it gets closer to the shaft end side whendeformation is insufficient at the tip of the shaft portion.Accordingly, by forming a concave having such a shape, deformationshortage at the tip portion of the shaft portion can be efficientlycompensated to form such a tip portion more accurately.

The shaft member having the above constitution can be provided as, forexample, a fluid lubrication bearing apparatus comprising this shaftmember; and a radial bearing gap formed between the outercircumferential surface of the shaft portion and the face facing it, theapparatus relatively rotatably supporting the shaft member by alubricating film of a fluid which occurs in a radial bearing gap.

Moreover, to achieve said third object, the present invention provides amethod for producing a metallic shaft member for fluid lubricationbearing apparatuses which comprises a shaft portion and a flangeportion, the shaft portion being formed by forging, the process of theforging comprising forming a concave by plastic processing on the tipface of the shaft portion to cause the tip portion of the shaft portionto overhang by a plastic flow.

As mentioned above, in the process of the forging of the shaft portion,when the concave is formed by plastic processing, for example, the tipportion of the shaft portion is preferably caused to overhang until itreaches at least final finished shape. Normally, the shaft member ofthis type is finished by grinding or like shaving process only at theportions where dimensional accuracy (shape accuracy) is required, amongforging formed articles. Accordingly, at the forging stage, the tipportion of the shaft portion is caused to overhang until at least afinal finished shape is reached so that the cutting process at the tipportion is enabled, and the shaft member having high dimensionalaccuracy can be thus obtained.

Various shapes are possible as a final finished shape of the tip of theshaft portion. For example, a shape defined by the outer circumferentialsurface of the tip of the shaft portion, the tip face of the shaftportion and a chamfer between these two faces is possible.

According to the present invention, when the shaft member is inrotation, the pressure balance in the thrust bearing gap formed on bothside of the flange portion in the axial direction can be restored in anearly stage and the thrust bearing gaps can be always maintained at apredetermined interval. Therefore, the rotational performance of thebearing can be exerted stably for a long term. Moreover, such a functioncan be obtained at low costs, and mass productivity can be dramaticallyimproved.

According to the present invention, the production of cutting powdersassociated with cutting is prevented. This prevents the deposition ofcontaminants to bearing component parts, disk crash, and contaminantsfrom getting inside a bearing apparatus as much as possible, maintainingthe cleanliness of the fluid lubrication bearing apparatus at low costs.Moreover, since the pin forming the prepared hole can be surely andaccurately pushed into the shaft material, the cylindricity of thethread portion can be maintained highly accurately, and the mountingaccuracy of other component screw fixed on the shaft member relative tothe shaft member can be improved.

According to the present invention, a shaft member for fluid lubricationbearing apparatuses which has high dimensional accuracy and can beelongated can be provided at low costs.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a side elevational view of a shaft member for hydrodynamicbearing apparatuses according to the first embodiment of the presentinvention.

FIG. 2 is a cross-sectional view of a spindle motor for an informationappliance integrating a hydrodynamic bearing apparatus comprising ashaft member.

FIG. 3 is a longitudinal sectional view of a hydrodynamic bearingapparatus.

FIG. 4 is a longitudinal sectional view of a bearing sleeve.

FIG. 5 is a lower end view of a bearing sleeve.

FIG. 6 is a side elevational view of a shaft material formed by aforging process.

FIG. 7 is a schematic illustration showing an example a grindingapparatus according to the width grinding step of a shaft material.

FIG. 8 is a partial cross-sectional view showing an example of agrinding apparatus according to the width grinding step.

FIG. 9 is a schematic illustration showing an example of a grindingapparatus according to the full face grinding process step of a shaftmaterial.

FIG. 10 is a schematic illustration showing an example of a grindingapparatus according to the grinding finish step of a shaft material.

FIG. 11 is a side elevational view of a shaft member for fluidlubrication bearing apparatuses according to the second embodiment ofthe present invention.

FIG. 12 is an expanded sectional view of the vicinity of the bottom of athreaded hole formed on the end of a shaft member.

FIG. 13 is a cross-sectional view of a spindle motor for informationappliances integrating a fluid lubrication bearing apparatus comprisinga shaft member.

FIG. 14 is a longitudinal sectional view of a fluid lubrication bearingapparatus.

FIG. 15 is a side elevational view of a shaft material formed by aforging process.

FIG. 16 is an expanded sectional view of the vicinity of the bottom of aprepared hole of a threaded hole formed the end of a shaft material.

FIG. 17 is a side elevational view of a shaft member for a fluidlubrication bearing apparatus according to the third embodiment of thepresent invention.

FIG. 18 is a cross-sectional view of a spindle motor for informationappliances integrating a fluid lubrication bearing apparatus.

FIG. 19 is a cross-sectional view of a fluid lubrication bearingapparatus.

FIG. 20 is a side elevational view of a shaft material formed by aforging process.

FIG. 21 is a schematic illustration of an example of a mold used in aforging process.

FIG. 22 is an expanded view which conceptionally shows a knownforming/forging manner of a shaft material.

FIG. 23 is an expanded view which conceptionally shows a forming/forgingmanner of a shaft material according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the present invention will be described below withreference to FIGS. 1-10.

FIG. 2 conceptionally shows an example of the constitution of a spindlemotor for information appliances incorporating a hydrodynamic bearingapparatus 1 according to the first embodiment of the present invention.This spindle motor for an information appliance is used for disk driveunits such as HDDs. It comprises the hydrodynamic bearing apparatus 1which rotatably supports a shaft member 2 in a non-contact manner; adisk hub 3 which is mounted on the shaft member 2; for example, a statorcoil 4 and a rotor magnet 5 facing each other across a gap in the radialdirection; and a bracket 6. The stator coil 4 is mounted on the outerperiphery of the bracket 6, and the rotor magnet 5 is mounted on theinner periphery of the disk hub 3. The bracket 6 has the hydrodynamicbearing apparatus 1 mounted on its inner periphery. Moreover, disk hub 3retains one or more disk-shaped information recording media such asmagnetic disks (hereinafter referred to simply as a disk) D on its outerperiphery. In the thus constructed spindle motor for informationappliances, when the stator coil 4 is energized, the rotor magnet 5 isrotated by the excitation between the stator coil 4 and rotor magnet 5.This causes the disk hub 3 and the disk D retained on the disk hub 3 torotate unitarily with the shaft member 2.

FIG. 3 shows an example of the hydrodynamic bearing apparatus 1. Thishydrodynamic bearing apparatus 1 is constituted of a housing 7 having abottom 7 b at its one end; a bearing sleeve 8 fixed on to the housing 7;a shaft member 2 inserted into the inner periphery of the bearing sleeve8; and a sealing member 9 as its main components. For the sake ofexplanation, the bottom 7 b side of the housing 7 is referred to as thelower side, and the side opposite to the bottom 7 b is referred to asthe upper side in the following description.

As shown in FIG. 3, the housing 7 is constituted of, for example, a sideportion 7 a formed of a resin material such as LCP, PPS, or PEEK in theform of a cylinder, and a bottom 7 b located at one end side of the sideportion 7 a and, for example, formed of a metallic material. In thisembodiment, the bottom 7 b is formed separately from the side portion 7a and is retrofitted on the lower inner periphery of the side portion 7a. In a part of the annular region of the upper end face 7 b 1 of thebottom 7 b, for example, a region in which a plurality of hydrodynamicgrooves are arranged spirally is formed as a portion for producinghydrodynamic pressure, although not shown in the Figs. Note that in thisembodiment, the bottom 7 b is formed separately from the side portion 7a, and fixed on the lower inner periphery of the side portion 7 a. Itcan be, however, formed integrally with the side portion 7 a, forexample, from a resin material. At this time, the hydrodynamic groovesprovided on the upper end face 7 b 1 can be die-formed simultaneouslywith the injection molding of the housing 7 comprising the side portion7 a and bottom 7 b, which can dispense with the trouble of forming thehydrodynamic grooves on the bottom 7 b.

The bearing sleeve 8 is formed, for example, of a porous body made of asintered metal, especially a porous body of a sintered metal comprisingcopper as a main ingredient in the form of a cylinder, and is fixed at apredetermined position the inner periphery face 7 c of the housing 7.

Throughout the inner periphery face 8 a of the bearing sleeve 8 or inpart of its cylinder face region, a hydrodynamic pressure producing partis formed. In this embodiment, for example, as shown in FIG. 4, theregion, in which a plurality of hydrodynamic grooves 8 a 1, 8 a 2 arearranged in a herringbone shape, is formed at two axially separatedpositions. In the region where of the upper hydrodynamic groove 8 a 1 isformed, the hydrodynamic groove 8 a 1 is formed asymmetrically in theaxial direction relative to the axial center m (the axial center of theregion between the upper and lower slanted grooves), the axial dimensionX1 of the region above the axial center m is larger than the axialdimension X2 of the region therebelow. Therefore, when the shaft member2 is in rotation, the lubricating oil in the radial bearing gap by theasymmetric hydrodynamic groove 8 a 1 is pushed downward.

On the outer circumferential surface 8 b of the bearing sleeve 8, one ormore axial direction grooves 8 b 1 are formed throughout its axiallength. In this embodiment, three axial direction grooves 8 b 1 areformed at an equal interval in the circumferential direction.

In the entire annular region of the lower end face 8C of the bearingsleeve 8 or apart thereof, a region in which a plurality of hydrodynamicgrooves 8 c 1 are arranged in a spiral shape is formed as a portion forproducing hydrodynamic pressure, for example, as shown in FIG. 5.

A sealing member 9 as a sealing means is formed, as shown in FIG. 3, forexample, of a soft metallic material such as brass and other metallicmaterials, or a resin material separately from the housing 7 and in anannular shape, and fixed by means of press fitting, adhesion or the likeinto the upper inner periphery of the side portion 7 a of the housing 7.In this embodiment, the inner periphery face 9 a of the sealing member 9is formed in the form of a cylinder, and the lower end face 9 b of thesealing member 9 is in contact with the upper end face 8 d of thebearing sleeve 8.

The shaft member 2 is, for example, formed of a metallic material suchas stainless steel, and has a T-shaped cross section integrallycomprising a shaft portion 21 and a flange portion 22 provided at thelower end of the shaft portion 21, as shown in FIG. 1. At the outerperiphery of the shaft portion 21, as shown in FIG. 3, radial bearingfaces 23 a, 23 b facing the region in which two hydrodynamic grooves 8 a1, 8 a 2 are formed on the inner periphery face 8 a of the bearingsleeve 8 are formed at two axially separated positions. Above one of theradial bearing faces, the face 23 a, a tapered face 24 whose diametergradually decreases toward the shaft tip is formed adjacently. Furtherthereabove, a cylinder face 25, which serves as a mounting portion ofthe disk hub 3, is formed. Annular recess portions 26, 27, 28 are formedbetween the two radial bearing faces 23 a, 23 b, between the otherradial bearing face 23 b and flange portion 22, and between the taperedface 24 and cylinder face 25, respectively.

On the upper end face of the flange portion 22, for example, a thrustbearing face 22 a of a first thrust bearing portion T1 facing the thrustbearing gap is formed, as shown in FIG. 3. On the lower end face of theflange portion 22, a thrust bearing face 22 b of a second thrust bearingportion T2 facing thrust bearing gap is formed, as shown in FIG. 3. Inaddition, on the inner diameter side (in the vicinity of the shaftportion 21) of the flange portion 22, a through-hole 29 opening to bothend faces of the flange portion 22 is formed. In this embodiment, thethrough-hole 29 opens to a portion on the inner diameter side of thethrust bearing faces 22 a, 22 b of both end faces of the flange portion22.

Between the tapered face 24 of the shaft portion 21 and the innerperiphery face 9 a of the sealing member 9 facing the tapered face 24,an annular sealing space S, whose radial dimension is graduallyincreased upwardly from the bottom 7 b side of the housing 7, is formed.In the hydrodynamic bearing apparatus 1 after being assembled (refer toFIG. 3), the inner space of the housing 7 containing the radial bearinggap and thrust bearing gap is completely filled with a lubricating oil,and its oil level is maintained to be within the range of the sealingspace S.

In the thus constructed hydrodynamic bearing apparatus 1, when the shaftmember 2 is rotated, the pressures of lubricating oil films formed inthe radial bearing gap between the regions (upper and lower) where thehydrodynamic grooves 8 a 1, 8 a 2 of the inner periphery face 8 a of thebearing sleeve are formed and the radial bearing faces 23 a, 23 b of theshaft portion 21 facing the region where these hydrodynamic grooves 8 a1, 8 a 2 are formed, respectively, are increased by the hydrodynamiceffect of the hydrodynamic grooves 8 a 1, 8 a 2. A first radial bearingportion R1 and a second radial bearing portion R2 which rotatablysupport the shaft member 2 in the radial direction in a non-contactmanner by the pressure of these oil films are then formed. Moreover, thepressure of the lubricating oil films formed in a first thrust bearinggap W1 (refer to FIG. 3) and in a second thrust bearing gap W2 (refer toFIG. 3) is increased by the hydrodynamic effect of the hydrodynamicgrooves. The first thrust bearing gap W1 is between a hydrodynamicgroove 8 c 1 region formed on the lower end face 8C of the bearingsleeve 8 and the upper (the shaft portion side) thrust bearing face 22 aof the flange portion 22 facing this hydrodynamic groove 8 c 1 region,while the second thrust bearing gap W2 is between the hydrodynamicgroove region formed on the upper end face 7 b 1 of the bottom 7 b andthe thrust bearing face 22 b on the lower side (opposite to the shaftportion side) of the flange portion 22 facing this hydrodynamic grooveregion. In addition, a first thrust bearing portion T1 and a secondthrust bearing portion T2, which rotatably support the shaft member 2 ina non-contact manner in the thrust direction, are formed by the pressureof these oil films.

When the shaft member 2 is in rotation, the lubricating oil circulatesin the above radial bearing gap W1 and thrust bearing gap W2, or betweenthe above gaps and the inside of the bearing sleeve 8 made of a porousbody, and the lubricating oil is appropriately provided for supportingthe shaft member in the bearing gaps. However, for some reason, thecirculation of the oil is sometimes disturbed. Also in that case, thethrough-hole 29 provided on the flange portion 22 adjusts the pressurebalance between the thrust bearing gaps W1, W2, whereby one thrustbearing gap (first thrust bearing gap W1) and the other thrust bearinggap (second thrust bearing gap W2) can be maintained at appropriateintervals. Accordingly, the shaft member 2 can be stably supported inthe thrust direction, enabling stable exertion of such bearingperformance for a long term.

A method for producing the shaft member 2 constituting the hydrodynamicbearing apparatus 1 will be described below.

The shaft member 2 is produced mainly in the following two steps: a (A)forming step and a (B) grinding step. The (A) forming step in thisprocedure comprises a shaft material forming process (A-1); athrough-hole forming process (A-2); and a shaft portion correctingprocess (A-3). Moreover, the (B) grinding step comprises a widthgrinding process (B-1); a full face grinding process (B-2); and a finishgrinding process (B-3).

(A) Forming Step

(A-1) Shaft Material Forming Process and (A-2) Through-Hole FormingProcess

To begin with, a metallic material such as stainless steel which will bea material of the shaft member 2 to be formed is compression-formed(forging process) by using molds, for example, in a cold state so that,for example, the shaft material 10 integrally having the regioncorresponding to the shaft portion (hereinafter referred to simply as ashaft portion) 11 and the region corresponding to the flange portion(hereinafter referred to simply as a flange portion.) 12 is formed(shaft material forming process (A-1)) as shown in FIG. 6. In thisembodiment, a mold used in forging of this shaft material 10 also servesas the mold for forming the through-hole 19 on the flange portion 12.Accordingly, by compression-forming the metal material with this mold, athrough-hole 19 passing between the side end face 12 a of the shaftportion of the flange portion 12 and the end face on the side oppositeto the shaft portion 12 b is formed (through-hole forming process (A-2))on the inner diameter side (in the vicinity of the shaft portion 11) ofthe flange portion 12 as the shaft material 10 is formed by forging, asshown in FIG. 6.

As mentioned above, performing the forming of the through-hole 19 on theflange portion 12 by a forging process can prevent cutting powders andthe like produced by processing, and dispense with or simplify acleaning step after the process. Moreover, the forming of thethrough-hole 19 and the forming of the shaft material 10 integrallycomprising the shaft portion 11 and flange portion 12 are performed bothby forging and simultaneously, whereby such a processing step can besimplified, and machining time can be greatly shortened.

A method of cold-forging employed in the above forming step may be,extrusion, upsetting, heading or the like, or combinations of them. Inthe examples shown in FIG. 6, the outer circumferential surface 11 a ofthe shaft portion 11 after being subjected to the forging process is ina different diameter shape comprising a tapered face 14 and a cylinderface 15 which is continuous upwardly with the tapered face 14 and has asmaller diameter than other portions disposed therebetween, but may beformed to have a uniform diameter throughout its length by dispensingwith the tapered face 14. Note that in this embodiment, described is thecase where the forming of the shaft material 10 and the forming of thethrough-hole 19 are performed both by a forging process simultaneously,both steps need not necessarily be performed simultaneously and thethrough-hole 19 may be formed by forging after forming the shaftmaterial 10 by forging.

(A-3) Shaft Portion Correcting Process

The shaft portion 11 of the shaft material 10 formed by forging in theprevious step is nipped with pressure, for example, with a pair ofrolling die (for example, flat dies and round dies, etc.) and said pairof rolling dies are reciprocated in the directions opposite to eachother to perform a rolling process for correcting cylindricity on theouter circumferential surface 11 a of the shaft portion 11 (shaftportion correcting process (A-3)), although not shown in the Figs. Thisimproves the cylindricity of the face 13 subjected to the correctingprocess, of the outer circumferential surface 11 a of the shaft portionof the shaft material 10 so that it falls within a required range (forexample, 10 μm or lower). Examples of the correcting processes of thecylindricity employed include a rolling process, drawing compound,ironing, sizing by pressing split-cavity molds (nipping) and variousother processing methods. Moreover, the correcting process is performednot only throughout the length of the outer circumferential surface 11 aof the shaft portion 11, but also on apart of the outer circumferentialsurface 11 a, as long as it includes the portions corresponding to theradial bearing faces 23 a, 23 b of the shaft member 2 as a finishedproduct.

(B) Grinding Step

(B-1) Width Grinding Process

The end face 11 b of the shaft portion and end face 12 b of the flangeportion 12 on the opposite side of the shaft portion, which will be theend faces of the shaft material 10 after being subjected to the formingstep, are ground relative to the corrected face 13 mentioned above. Agrinding apparatus 40 used in this grinding step comprises, for example,a carrier 41 which retains a plurality of the shaft material 10 asworkpiece; and a pair of grind stones 42, 42 which grinds the end face11 b of the shaft portion and end face 12 b of the flange portion 12 onthe opposite side of the shaft portion of the shaft material 10 retainedby the carrier 41, as shown in FIG. 7.

As shown in FIG. 7, a plurality of notches 43 is provided on part of thecircumferential region of the outer periphery of the carrier 41 at anequal pitch in the circumferential direction. The shaft material 10 iscontained in the notch 43 with its correcting process face 13 in angularcontact with the inner face 43 a of the notch 43. The correcting processface 13 of the shaft material 10 protrudes slightly from the outercircumferential surface of the carrier 41, and a belt 44 is provided onthe outer diameter side of the carrier in a tensioned state to bind theprotruding portions of the shaft material 10 from the outer diameterside. On both axial end sides of the carrier 41 where the shaft material10 is contained in the notch 43, for example, a pair of grind stones 42,42 are coaxially disposed with their end faces (grinding surfaces)facing each other at a predetermined interval, as shown in FIG. 8.

As the carrier 41 rotates, the shaft material 10 is sequentially loadedinto the notch 43 from a determined position. The loaded shaft material10 traverses the end faces of the rotating grind stones 42, 42 fromtheir outer diameter edge toward the inner diameter edge in such a statethat it is prevented from falling off from the notch 43 by binding ofthe belt 44. Accordingly, both end faces of the shaft material 10, i.e.,the end face 11 b of the shaft portion and the end face 12 b of theflange portion 12 on the side opposite to the shaft portion are groundby the end faces of the grind stones 42, 42 (refer to FIG. 8). At thistime, the corrected face 13 of the shaft material 10 is supported by thecarrier 41 and this corrected face 13 has high cylindricity. Therefore,if the perpendicularity of the rotation axis of the grind stone 42 andthe grinding surface of the grind stone 42 and the parallelism of therotation axis of the grind stone 42 and the rotation axis of the carrier41, etc. are highly accurately controlled in advance, both end faces 11b, 12 b of the shaft material 10 can be highly accurately finished withreference to this corrected face 13, enabling to suppress the value ofthe perpendicularity relative to the corrected face 13. Moreover, thewidth of the shaft material 10 in the axial direction (the overalllength including the flange portion 12) can be finished to have apredetermined size.

(B-2) Full Face Grinding Process

Subsequently, the outer circumferential surface 10 a of the shaftmaterial 10 and the side end face 12 a of the flange portion 12 on theshaft portion side are ground relative to both end faces (the end face11 b of the shaft portion, the end face 12 b of the flange portion 12 onthe side opposite to the shaft portion) of the ground shaft material 10.The grinding apparatus 50 used in this grinding step performs, forexample, plunge-grinding by the grind stone 53 with the back plate 54and pressure plate 55 pressed to both end faces of the shaft material10, as shown in FIG. 9. The corrected face 13 of the shaft material 10is rotatably supported by a shoe 52.

The grind stone 53 is a formed grind stone which comprises a grindingsurface 56 corresponding to the outer circumferential surface shape ofthe shaft member 2 as a finished product. The grinding surface 56comprises a cylinder grinding portion 56 a which grinds the outercircumferential surface 11 a through the length of the shaft portion 11in the axial direction and the outer circumferential surface 12 c of theflange portion 12; and a plane grinding portion 56 b which grinds theside end face 12 a of the shaft portion of the flange portion 12. Thegrind stone 53 in the example shown in FIG. 9 comprises, as the cylindergrinding portion 56 a, portions 56 a 1, 56 a 2, which grind the regionscorresponding to the radial bearing faces 23 a, 23 b of the shaft member2, a portion 56 a 3, which grinds the region corresponding to thetapered face 24, a portion 56 a 4, which grinds the region correspondingto the cylinder face 25, portions 56 a 5-56 a 7, which grind the recessportions 26-28, respectively, and a portion 56 a 8, which grinds aregion corresponding to the outer circumferential surface 22 c of theflange portion 22.

Grinding in the grinding apparatus 50 of the above constitution isperformed in the following procedure. To begin with, the grind stone 53is fed obliquely (the direction of arrow 1 in FIG. 9) with the shaftmaterial 10 and grind stone 53 rotating, and a plane grinding portion 56b of grind stone 53 is pressed against the side end face 12 a on theshaft portion side of the flange portion 12 to grind the side end face12 a on the shaft portion side of the flange portion 12. The finishingprocess of the end face of the flange portion 22 of the shaft member 2on the shaft portion side is thus completed, forming the thrust bearingface 22 a facing a first thrust bearing portion T1. Subsequently, thegrind stone 53 is fed in the direction perpendicular to the rotationaxis of the shaft material 10 (the direction of arrow 2 in FIG. 9), andthe cylinder grinding portion 56 a of the grind stone 53 is pressed tothe outer circumferential surface 11 a of the shaft portion 11 of theshaft material 10 and the outer circumferential surface 12 c of theflange portion 12 to grind the faces 11 a, 12 c. Accordingly, out of theouter circumferential surface of the shaft portion 21 of the shaftmember 2, the regions corresponding to radial bearing faces 23 a, 23 band cylinder face 25 are ground respectively, and the tapered face 24,the outer circumferential surface 22 c of the flange portion 22, and therecess portions 26-28 are formed. Note that in the above grinding, forexample, it is preferred to perform grinding while measuring theremaining grinding allowance by a measurement gauge 57, as shown in FIG.9.

In this full face grinding process step, since the accuracy setting ofthe perpendicularity of both end faces 11 b, 12 b of the shaft material10 has been performed beforehand in the width grinding, each of theto-be-ground surfaces can be ground highly accurately.

(B-3) Finish Grinding Process

(B-2) Among the faces which have been ground in full face grindingprocess, the radial bearing faces 23 a, 23 b of the shaft member 2 andthe region corresponding to the cylinder face 25 are subjected to thefinal finish grinding process. An example of the grinding apparatus usedin this grinding is a cylinder grinder shown in FIG. 10. It performsplunge grinding by the grind stone 63, while rotating the shaft material10 held between the back plate 64 and pressure plate 65. The shaftmaterial 10 is rotatably supported by a shoe 62. A grinding surface 63 aof the grind stone 63 comprises a first cylinder grinding portion 63 a 1which grinds regions corresponding to the radial bearing faces 23 a, 23b of the shaft member 2 (the regions 13 a, 13 b in FIG. 10), and asecond cylinder grinding portion 63 a 2 which grinds a regioncorresponding to the cylinder face 25 (region 15 in FIG. 10).

In the grinding apparatus 60 having the above constitution, by providingthe rotating grind stone 63 with the feed in the radial direction, theregions 13 a, 13 b, and 15 corresponding to the radial bearing faces 23a, 23 b and cylinder face 25, respectively, are ground, and theseregions are finished to have the final surface accuracy.

After the above (A) forming step and (B) grinding step are finished,heat treatment and cleaning process, if necessary, can be performed tocomplete the shaft member 2 shown in FIG. 1. Accordingly, in thevicinity of the shaft portion 21, a through-hole 29 opening to both endfaces of the flange portion 22 is formed. Since the inner periphery faceof the through-hole 29 is formed by a forging process, its surfaceroughness becomes high.

According to the above production method, the cylindricity of the radialbearing faces 23 a, 23 b formed on the outer periphery of the shaftportion 21 can be finished highly accurately. Because of this, forexample, the circumferential or axial variation of the radial bearinggap formed between the inner periphery face 8 a of the inner peripheryof the bearing sleeve 8 of in the hydrodynamic bearing apparatus 1 anditself is suppressed to be in a predetermined range, and bearingperformance can be thus prevented from being adversely affected by thevariation of the above radial bearing gap. Moreover, relative to theradial bearing faces 23 a, 23 b formed on the outer periphery of theshaft portion 21, the shaft member 2 whose values of theperpendicularity of both end faces 22 a, 22 b of the flange portion 22(thrust bearing face) are suppressed can also be formed. Because thethrust bearing faces 22 a, 22 b formed on both end faces of the flangeportion 22 form the thrust bearing gap between themselves and the facesfacing them (the lower end face 8C of the bearing sleeve 8, the upperend face 7 b 1 of the bottom 7 b of the housing 7, etc.), the numericalvalue of such perpendicularity can be thus suppressed to a low level,whereby variation in the above thrust bearing gap can be reduced.Moreover, the end face of the shaft portion 21 b can also serve as thereference plane for setting the above thrust bearing gap. Accordingly,by suppressing the numerical value of the perpendicularity of the endface 21 b of the shaft portion to a low level, the thrust bearing gapcan be controlled with high accuracy.

Moreover, in this embodiment, since a finish grinding process (refer toFIG. 10) is performed in the region corresponding to the cylinder face25 of the shaft portion 21, the cylindricity of the cylinder face 25 canalso be finished highly accurately, the mounting accuracy in mountingcomponents such as the disk hub 3 to the shaft member 2 can beincreased. Because of this, the accuracy when clampers or the like forretaining the disk D on the disk hub 3 is fixed on the shaft member 2can be increased, and the mounting accuracy relative to the shaft member2 of the disk D clamped between the clamper and disk hub 3 can befurther increased, thereby further improving the motor performance.

Described in the above embodiment is the case where the through-hole 29is formed so that it opens to the inner diameter side of these bearingface 22 a, 22 b to prevent a drop in the pressure in the thrust bearinggaps W1, W2, avoiding the thrust bearing faces 22 a, 22 b of the flangeportion 22 (thrust bearing gaps W1, W2). However, when the hydrodynamicgrooves and thrust bearing gaps can be set considering some pressuredrop, the through-hole 29 can also be formed in such positions on thethrust bearing faces 22 a, 22 b.

A second embodiment of the present invention will be described belowwith reference to FIGS. 11-16. Note that portions and components havingthe same constitution and actions as the constitutions shown in FIGS.1-10 (first embodiment) are referred to by the same reference numerals,and their repeated explanations are omitted.

FIG. 13 conceptionally shows an example of the constitution of a spindlemotor for information appliances incorporating a fluid lubricationbearing apparatus (hydrodynamic bearing apparatus) 101 according to thesecond embodiment of the present invention. This spindle motor forinformation appliances is used for disk drive units such as HDDs, andcomprises a fluid lubrication bearing apparatus 101 which rotatablysupports a shaft member 102 in a non-contact manner; a disk hub 3mounted on the shaft member 102, a stator coil 4 and a rotor magnet 5which, for example, face each other across a gap in the radialdirection; and a bracket 6. The stator coil 4 is mounted on the outerperiphery of the bracket 6, and the rotor magnet 5 is mounted on theinner periphery of the disk hub 3. The bracket 6 has a fluid lubricationbearing apparatus 101 attached on its inner periphery. Moreover, thedisk hub 3 retains one or more disk D such as magnetic disks on itsouter periphery, and the disk D is held between the disk hub 3 and aclamper 110. In this spindle motor for an information appliance, whenthe stator coil 4 is energized, the rotor magnet 5 is rotated by themagnetic force between the stator coil 4 and rotor magnet 5, whereby thedisk hub 3, shaft member 102 and the disk D held between the disk hub 3and clamper 110 are rotated unitarily.

FIG. 14 shows an example of the fluid lubrication bearing apparatus 101.This fluid lubrication bearing apparatus 101 is constituted of a housing7 having a bottom 7 b at its one end; a bearing sleeve 8 fixed on thehousing 7 as a sleeve member; a shaft member 102 inserted into the innerperiphery of the bearing sleeve 8; and a sealing member 9, as its maincomponents. For the sake of explanation, the bottom 7 b side of thehousing 7 is referred to as the lower side, and the side opposite to thebottom 7 b is referred to as the upper side in the followingdescription.

The shaft member 102 is formed, for example, of a metallic material suchas stainless steel, and has a T-shaped cross section integrallycomprising a shaft portion 121 and a flange portion 122 provided at thelower end of the shaft portion 121, as shown in FIG. 11. On the outerperiphery of the shaft portion 121, as in the first embodiment, radialbearing faces 123 a, 123 b facing the region in which two hydrodynamicgrooves 8 a 1, 8 a 2 are formed on the inner periphery face 8 a of thebearing sleeve 8 are formed at two axially separated positions, as shownin FIG. 4. Above one them, the radial bearing face 123 a, a tapered face124, of which diameter gradually decreases toward the shaft tip, isformed adjacently, and a cylinder face 125, which serves as a mountingportion of the disk hub 3, is formed further thereabove. Annular recessportions 126, 127, 128 are formed between the two radial bearing faces123 a, 123 b, between the other radial bearing face 123 b and flangeportion 122, and between the tapered face 124 and the cylinder face 125,respectively.

In the shaft portion 121, on the axis of the end face 121 b on the sideopposite to the flange portion 122, a threaded hole 131 for screwing theclamper 110 on the shaft member 2 is formed. A thread portion 132 whichscrews together with screw 111 for fixing the clamper 110 on the innerperiphery on the opening side of the hole 131 is formed, and forexample, a prepared hole 133 formed prior to the formation of the threadportion 132 at the bottom of the threaded hole 131 as shown in FIG. 12is remaining.

The disk hub 3 is fixed on the cylinder face 125 formed on the upper endof the shaft portion 121 of the above shaft member 102 by, for example,adhesion, press fitting or other means. In addition, the screw 111 isscrewed into the threaded hole 131 formed on the shaft portion 121 viathe clamper 110 so that the clamper 110 is fixed on the disk hub 3, andthe disk is held between the clamping faces 3 a, 110 a formed on theouter diameter side the upper face of the disk hub 3 and on the outerdiameter side of the lower surface of the clamper 110.

In such a manner mentioned above, the fluid lubrication bearingapparatus 101 retaining the disk D on the disk hub 3 is constituted asshown in FIG. 14. At this time, an annular sealing space S, whose sizein the radial direction is gradually increased upwardly from the bottom7 b side of the housing 7, is formed between the tapered face 124 of theshaft portion 121 and the inner periphery face 9 a of a sealing member 9facing the tapered face 124. In the fluid lubrication bearing apparatus101 after being assembled (refer to FIG. 14), the oil level is retainedwithin the range of the sealing space S.

In the thus constructed fluid lubrication bearing apparatus 101, whenthe shaft member 102 is rotated, the pressures of lubricating oil filmsformed in the radial bearing gaps between the radial bearing faces 123a, 123 b of the shaft portion 121 facing the regions (upper and lower)where the hydrodynamic grooves 8 a 1, 8 a 2 are formed on the innerperiphery of the bearing sleeve face 8 a and the region where thesehydrodynamic grooves 8 a 1, 8 a 2 are formed, respectively, areincreased by the hydrodynamic effect of the hydrodynamic grooves 8 a 1,8 a 2. In addition, a first radial bearing portion R11 and a secondradial bearing portion R12 which rotatably support the shaft member 102in the radial direction in a non-contact manner are formed by thepressure of these oil films. Moreover, the pressures of lubricating oilfilms formed in a first thrust bearing gap between the thrust bearingface 122 a of the upper side (the shaft portion side) of the flangeportion 122 facing the region where the hydrodynamic groove 8 c 1 isformed on the lower end face 8 c of the bearing sleeve 8 and the regionwhere this hydrodynamic groove 8 c 1 is formed, and in a second thrustbearing gap between the region where the hydrodynamic groove is formedon the upper end face 7 b 1 of the bottom 7 b, the thrust bearing face122 b on the lower side (opposite to the shaft portion side) the flangeportion 122 facing this face are increased by the hydrodynamic effect ofthe hydrodynamic grooves. In addition, a first thrust bearing portionT11 and a second thrust bearing portion T12 which rotatably support theshaft member 102 in the thrust direction in a non-contact manner areformed by the pressure of these oil films.

The production method of the shaft member 102 constituting the abovefluid lubrication bearing apparatus 101 will be described below.

The shaft member 102 is produced in mainly two steps: a (C) forming stepand a (D) grinding step. In this procedure, the (C) forming stepcomprises a forging process (C-1), a thread portion rolling process(C-2) and a correcting process (C-3). The (D) grinding step comprises awidth grinding (D-1), a full face grinding process (D-2), and a finishgrinding process (D-3).

(C) Forming Step

(C-1) Forging Process

To begin with, a material of the shaft member 102 to be formed, i.e., ametal material such as stainless steel is subjected tocompression-forming (plastic deformation) with a mold, for example, in acold state, whereby, for example, the shaft material 112 integrallyhaving the region corresponding to the shaft portion (hereinafterreferred to simply as a shaft portion) 113 and the region correspondingto the flange portion (hereinafter referred to simply as a flangeportion.) 114 is formed (forging process), as shown in FIG. 15.Moreover, the prepared hole 133 for forming the threaded hole 131 isformed by forging (for example, backward extrusion) on the edge of theshaft portion 113 as the shaft material 112 is formed by the forgingprocess mentioned above (refer to FIG. 11).

At this time, on the inner periphery of the prepared hole 133 formed byforging simultaneously with the shaft material 112, a cylinder face 134whose diameter is constant is formed as shown in FIG. 15, and a conicalsurface 135 which is continuous with the cylinder face 134 is formed atits bottom. In a connecting portion 134 a between the conical surface135 and cylinder face 134, a radially curved surface which smoothlyconnects the conical surface 135 and cylinder face 134 as shown in FIG.16 is formed. Moreover, at a top 135 a of the conical surface 135, aradially curved surface is formed similarly. From a differentperspective, these are plastically deformed in conformity with the tipshape of the pin pushed into the metallic material in forging of theprepared hole 133. That is, although not shown in the Figs., a conicalsurface is formed at the tip of the pin, and a cylinder face is formedon the outer periphery of the pin, the connecting portion between theconical surface and the outer circumferential surface of the cylinderand the top of the conical surface has the shape of a rounded edge (bothhave a radially curved surface shape herein).

Such a pin shape (in this embodiment, the connecting portion between theconical surface and cylinder face of the pin and the top of the conicalsurface are each caused to be a radially curved surface), when the pinis pushed into the metallic material, concentrated stress at a portioncorresponding to the connecting portion 134 a of the metallic material(shaft material 112) or a portion corresponding to top 135 a ismitigated. This can increase the yield rate in forming of the preparedhole 133 (in the forging process), and ensure the forming of theprepared hole 133. Moreover, for example, a radially curved surface isformed at the connecting portion 134 a or top 135 a, the diameter of theradially curved surface can be large enough to maintain the guidefunction of the pin of the conical surface 135 when the pin is pushedin. Because of this, the stress at a portion corresponding to theconnecting portion 134 a or a portion corresponding to the top 135 awhen the pin is pushed in can be mitigated, while the guide function ofthe conical surface formed at the tip of the pin when it is pushed intothe processed material regarding the pushing direction is provided,enabling secure and accurate forming of the prepared hole 133.

As mentioned above, when the prepared hole is formed by forging, itsreduction of area should be also noted. Reduction of area refers to theratio of a cross section area of a material after being processed tothat of the material before being processed. As in this embodiment, whenthe prepared hole 133 is formed by forging (mainly extrusion) on the barmetallic material (shaft material 112), assuming that the edge outerdiameter of the shaft portion 113 in the shaft material 112 is d1 andthe hole diameter of the prepared hole 133 formed by forging is d2,reduction in excess RA is, for example, represented byRA=(πd2²/4)/(πd1²/4)×100[%], as shown in FIG. 15.

Since the forging basically performs compression forming of the materialwhich will be the target to be processed, required processing pressure,or processable processing pressure is affected by the ductility andstrength of the processed material, and durability (wear resistance,strength, etc.) of the mold. Therefore, to obtain sufficient dimensionalaccuracy while ensuring moldability under this condition, a dimensionallimit of processing inevitably occurs. From these perspectives, forexample, when a steel material such as stainless steel is used as a rawmaterial of the processed material (shaft material 112), the reductionin excess RA is preferably within the range of 20%-75%. The upper limitof this is preferably 70%, while the lower limit value is morepreferably 25%. Moreover, there is also an appropriate range of theaxial length of the prepared hole 133 formed for the reason mentionedabove. For example, the dimension of the prepared hole 133 (aspectratio) is preferably set so that the axial length (depth) E falls withinthe range of 2.0×d2−3.0×d2 at its maximum.

Moreover, in the forging process of the shaft material 112, depending onthe shape of the shaft material 112 and the manner that it is formed,compressive force is not sufficiently transmitted to the tip portion ofthe shaft material 112, deformation may be insufficient at the tipportion. In contrast, in this embodiment, the prepared hole 133 of thethreaded hole 131 is formed by forging at the tip portion of the shaftportion 113 simultaneously with forging of the shaft material 112, thematerial which was previously in the prepared hole 133 is pushed out tothe surrounding of the prepared hole 133 to cause the tip portion tooverhang on the outer diameter side and shaft end side. Accordingly, thetip portion can be formed preventing deformation shortage at the tipportion of the shaft material 112 as much as possible in forging.

Note that a method of cold forging employed in the above forming stepmay be the extrusion mentioned above (forward extrusion and backwardextrusion), upsetting, heading or the like, or combinations of them. Inthe examples shown in FIG. 15, the outer circumferential surface 113 aof the shaft portion 113 after the forging process is in a differentdiameter shape which comprises a tapered face 115 and a cylinder face 15continuous upwardly with the tapered face 115 and having a diameter thanother portions disposed therebetween, but the tapered face 115 may bedispensed with and formed to have a uniform diameter throughout itslength.

(C-2) Thread Portion Rolling Process

In the prepared hole 133 of the shaft material 112 formed by forging inthe preceding step, for example, while a rolling tool such as a rolledtap is relatively rotated between the shaft material 112 and the tapitself is pushed into the prepared hole 133, although not shown in theFigs. Because of this, the outer peripheral shape of the rolled tap isrolled to the cylinder face 134 of the inner periphery of the preparedhole 133, whereby the valley 132 a of the thread portion 132 is formedand the material portion pushed out by the rolling of the valley 132 abulges on its adjacent region, the peak 132 b of the thread portion 132is formed (refer to FIG. 15 or 16).

As mentioned above, the prepared hole 133 to form the threaded hole 131is formed by forging so that the thread portion 132 can be formed byrolling on the inner periphery of the prepared hole 133 formed byforging, that is, the threaded hole 131 is formed by plastic processing.Therefore, chips (cutting powders, etc.) caused by cutting or likemachining can be greatly reduced. Accordingly, it is possible to preventchips from being deposited on other parts constituting the bearing(including constitutional parts of the motor) as contaminants inassembly, for example, getting in the lubricating oil filling the insideof the fluid lubrication bearing apparatus 101 while in use, or beingtransferred to the disk D to cause disk crash. Moreover, since the shaftmaterial 112 and the prepared hole 133 of the threaded hole 131 areformed in a common forging step, such a forming step can be simplifiedand processing costs can be reduced. In addition, chips or other wastecan be prevent before and after the forming process, whereby materialscan be efficiently used to greatly cut on material costs. Alternatively,cycle time can be shortened by employing forging processes and rollingprocesses, improving the productivity.

(C-3) Correcting Process

To increase the dimensional accuracy of the shaft material 112 formed bya forging process, in particular the cylindricity of the facecorresponding to the outer circumferential 113 a surface of the shaftportion the shaft member 102 as a finished product (hereinafter simplyreferred to as the outer circumferential surface of the shaft portion),the outer circumferential surface 113 a of the shaft portion of theshaft material 112 is subjected to a plastic processing for correctingthe cylindricity after the forging process. Because of this, out of theouter circumferential surface 113 a of the shaft portion of the shaftmaterial 112, the outermost diameter surface 117 of the shaft portion113 is corrected, the cylindricity of the face 117 subjected to thecorrecting process is improved to be in a desired range (for example, 10μm or lower). Simultaneously, the cylinder face 116 of the upper end ofthe shaft portion 113 is also subjected to a correcting process, wherebythe cylindricity of the cylinder face 116 is improved similarly. Notethat as the correcting process of the cylindricity, rolling, drawing,ironing, sizing by pressing split-cavity molds (nipping) or variousother processing methods can be employed.

(D) Grinding Step

(D-1) Width Grinding

Both end faces of the shaft material 112 which have been subjected tothe correcting process, i.e., the end face 113 b of the shaft portionand the end face 114 b of the flange portion 114 on the side opposite tothe shaft portion (refer to FIG. 15) are ground relative to theoutermost diameter surface 117 subjected to said correcting process outof the outer circumferential surface 113 a of the shaft portion (thefirst grinding step). The grinding apparatus used in this grinding stepcomprises, as in the first embodiment, a carrier 41 retaining aplurality of the shaft materials 112 as workpieces; and a pair of grindstones 42, 42 which grind the end face 113 b of the shaft portion of theshaft material 112 retained by the carrier 41 and the end face 114 b ofthe flange portion 114 on the side opposite to the shaft portion, asshown in FIGS. 7 and 8. Note that other constitutions of the grindingapparatus 40 than this are based on the first embodiment, and theirexplanations are thus omitted.

As the carrier 41 rotates, the shaft material 112 is loaded into thenotch 43 a sequentially from a certain position. The loaded shaftmaterial 112 traverses the end faces of the rotating grind stones 42, 42from their outer diameter edge toward the inner diameter edge in such astate that it is prevented from falling off from the notch 43 by bindingof the belt 44. Accordingly, both end faces of the shaft material 112,namely the end face 113 b of the shaft portion an the end face 114 b ofthe flange portion 114 on the side opposite to the shaft portion, areground by the end face s of the grind stones 42, 42. Moreover, the widthof the shaft material 112 in the axial direction (the entire lengthincluding the flange portion 114) is finished to have a predeterminedsize.

(D-2) Full Face Grinding Process

Subsequently, the outer circumferential surface 112 a of the shaftmaterial 112 and the end face 114 a of the flange portion 114 on theshaft portion side are ground relative to the ground end faces 113 b,114 b of the shaft material 112 (both end faces 121 b, 122 b of theshaft member 102) (the second grinding step). As in the firstembodiment, the grinding apparatus used in this grinding step performsplunge-grinding by the grind stone 53 with the back plate 54 andpressure plate 55 pressed against both end faces of the shaft material112, as shown in FIG. 9. The correcting process face 117 of the shaftmaterial 112 is rotatably supported by a shoe 52. Note that otherconstitutions of the grinding apparatus 50 than this is based on thefirst embodiment, and their explanations are thus omitted.

Grinding in the grinding apparatus 50 of the above constitution isperformed in the following procedure. To begin with, while the shaftmaterial 112 and the grind stone 53 are in rotation, the grind stone 53is fed obliquely (the direction of arrow 1 in FIG. 9), a plane grindingportion 56 b of the grind stone 53 is pressed against the end face 114 aof the flange portion on the shaft portion side of the shaft material112 to grind mainly the end face 114 a on the shaft portion side. Theshaft portion side end face 122 a in the flange portion 122 of the shaftmember 102 is thus formed. Subsequently, the grind stone 53 is fed inthe direction perpendicularly intersecting the rotation axis of theshaft material 112 (the direction of arrow 2 in FIG. 9), and then thecylinder grinding portion 56 a of the grind stone 53 is pressed againstthe outer circumferential surface 113 a of the shaft portion 113 of theshaft material 112 and the outer circumferential surface 114C of theflange portion 114 to grind the faces 113 a, 114C. Accordingly, out ofthe outer circumferential surface of the shaft portion 121 of the shaftmember 102, the radial bearing faces 123 a, 123 b and the regioncorresponding to the cylinder face 125 are ground and the tapered face124, the outer circumferential surface 122C of the flange portion 122,and the recess portions 126-128 are further formed.

(D-3) Finish Grinding Process

(D-2) Among the faces which have been ground in the full face grindingprocess, the radial bearing faces 123 a, 123 b of the shaft member 102and the region corresponding to the cylinder face 125 are subjected tothe final finish grinding process. As in the first embodiment, agrinding apparatus used in this grinding performs plunge grinding on therotating shaft material 112 held between the back plate 64 and pressureplate 65 by the grind stone 63 with the cylinder grinder shown in FIG.10. Note that other constitutions of the grinding apparatus 60 are basedon the first embodiment, and their explanations are thus omitted.

In the grinding apparatus 60 having the above constitution, the radialbearing faces 123 a, 123 b and the region corresponding to the cylinderface 125 are ground by providing the rotating grind stone 63 with thefeed in the radial direction, and these regions are finished to have thefinal surface accuracy.

After the above (C) forming step and (D) grinding step, heat treatmentand cleaning process, if necessary, are performed so that the shaftmember 102 shown in FIG. 11 is completed.

The shaft member 102, as long as it is produced by the above productionmethod, by forming the prepared hole 133 with high accuracy, the formingaccuracy of the threaded hole 131, for example, the coaxiality of thecenter line of the pitch circle of the thread portion relative to theaxis of the shaft member 102 can be suppressed to 0.2 mm or lower.Moreover, according to the above production method, relative to theradial bearing faces 123 a, 123 b formed on the outer periphery of theshaft portion 121, it is also possible to form the shaft member 102 withsuppressed perpendicularity of both end faces 122 a, 122 b of the flangeportion 122 (thrust bearing face) and suppressed value of theperpendicularity of the end face 121 b of the of the shaft portion.Among these, the end face 121 b of the shaft portion not only serves asa reference plane for grinding the outer circumferential surface of theshaft portion 121 and the upper end face of the flange portion 122(thrust bearing face 122 a side), but also serves as a contact surfacewhen the clamper 110 which holds the disk D between the disk hub 3 anditself to fix it is fixed on the shaft member 102 (screw fixing).

Accordingly, as mentioned above, the forming accuracy of the threadedhole 131 (in particular, the coaxiality of the thread portion 132) canbe increased, and the value of the perpendicularity of the end face 121b of the of the shaft portion can be also suppressed to a low level,whereby the mounting accuracy on the shaft member 102 of the clamper 110can be increased. As a result, the disk D can be fixed with the value ofthe perpendicularity relative to the shaft member 102 suppressed to alow level, and runout of the disk D relative to the shaft member 102when the shaft member 102 is in rotation can be suppressed. Hence,excellent disk rotation can be obtained.

According to the above production method, the cylindricity of the radialbearing faces 123 a, 123 b formed on the outer periphery of the shaftportion 121 can also be finished highly accurately. Because of this, forexample, variation in the circumferential or axial dimension of theradial bearing gap formed between the inner periphery of the bearingsleeve 8 in the fluid lubrication bearing apparatus 101 and the outerperiphery of the shaft portion 121 can be suppressed to be in apredetermined range, and the bearing performance can be thus preventedfrom being adversely affected by the variation of the above radialbearing gap. Furthermore, the region corresponding to the cylinder face125 of the shaft portion 121 is subjected to the finish grinding process(refer to FIG. 10) so that the cylindricity of the cylinder face 125 canalso be finished highly accurately, increasing the mounting accuracy inmounting the disk hub 3 or other components on the shaft member 102.This can further increase the mounting accuracy of the clamper 110 andthe disk D clamped between the clamper 110 and disk hub 3 relative toshaft member 102, thereby further improving the motor performance.

Note that the example described in the above embodiment is soconstructed that a radially curved surface is formed in the preparedhole 133 at the connecting portion 134 a between the conical surface 135and cylinder face 134 and that a radially curved surface is formed onthe top 135 a of the conical surface 135, but it is not limited to thisconfiguration. For example, as for the connecting portion 134 a, theremay be formed any face as long as the it smoothly connects the conicalsurface 135 and the cylinder face 134. Moreover, as for the top 135 a,there may be formed any face as long as the top 135 a is removed fromthe top 135 a, for example, a flat face where the top 135 a is removed(truncated conical surface) may be formed instead of a radially curvedsurface.

A third embodiment of the present invention will be described below withreference to FIGS. 17-23.

FIG. 18 conceptionally shows one constitutional example of a spindlemotor for information appliances incorporating a fluid lubricationbearing apparatus 201 according to the third embodiment of the present.This spindle motor is used for disk drive units such as HDDs, andcomprises a fluid lubrication bearing apparatus (hydrodynamic bearingapparatus) 201 which rotatably supports the shaft member 202 fixing thehub 203 in a non-contact manner; for example, a stator coil 204 and arotor magnet 205 opposing each other across a gap in the radialdirection; and a bracket 206. The stator coil 204 is mounted on theouter diameter side of the bracket 206, and the rotor magnet 205 ismounted on outer periphery of the hub 203. The bearing component 207 ofthe fluid lubrication bearing apparatus 201 is fixed on the innerperiphery of the bracket 206. Moreover, one or more of the disk D isretained on the hub 203. In FIG. 18, two of the disk D is retained onthe hub 203. In the thus constructed spindle motor, when the stator coil204 is energized, the rotor magnet 205 is rotated by the excitationproduced between the stator coil 204 and rotor magnet 205, whereby thedisk D retained on the shaft member 202 and the hub 203 which is fixedon shaft member 202 are rotated unitarily with the shaft member 202.

FIG. 19 shows the fluid lubrication bearing apparatus 201. This fluidlubrication bearing apparatus 201 mainly comprises a bearing component207 whose one end opens, a shaft member 202 which is inserted at theinner periphery of the bearing component 207 and rotates relative to thebearing component 207. Note that for the sake of explanation, the sideof a bottom 209 b of the housing portion 209 constituting the bearingcomponent 207 is referred to as the lower side, while the side oppositeto the bottom 209 b is referred to as the upper side in the descriptionbelow.

The bearing component 207 has such a shape that it opens at least at oneaxial end, and separately comprises an approximately cylindrical sleeveportion 208 and a housing portion 209 positioned on the outer diameterside of the sleeve portion 208 in this embodiment.

The sleeve portion 208 is, for example, formed in the form of a cylinderwith a metallic non-porous body or a porous body made of a sinteredmetal. In this embodiment, the sleeve portion 208 is formed in the formof a cylinder form with a porous body made of a sintered metalcomprising copper as a main ingredient, and is fixed on the innerperiphery face (large diameter face 209 c) of the housing portion 209by, for example, adhesion (including loose adhesion and press fittingadhesion), press fitting, welding (for example, ultrasonic welding) orother suitable means. Of course, the sleeve portion 208 can be alsoformed from non-metallic materials such as resins, ceramics, etc.

On the entire surface of the inner periphery face 208 a of the sleeveportion 208 or a part thereof a cylinder region, a region in which aplurality of hydrodynamic grooves are arranged is formed. In thisembodiment, for example, a region in which a plurality of hydrodynamicgrooves is arranged in a herringbone shape is formed at two axiallyseparated positions, as in FIG. 4.

In the entire annular region of the lower end face 208 b of the sleeveportion 208 or a part thereof, a region in which a plurality ofhydrodynamic groove are spirally arranged as a portion for producingthrust hydrodynamic pressure, for example, as in FIG. 5, is formed. Thisregion in which the hydrodynamic grooves are formed faces the upper endface 222 a of the flange portion 222 as a thrust bearing face. While theshaft member 202 is in rotation, the region forms the thrust bearing gapof a first thrust bearing portion T21 described later between the itselfand the upper end face 222 a (refer to FIG. 19).

The housing portion 209 is formed of a metal or a resin, and has acylinder part 209 a, and a bottom 209 b integrally or separately formedat the lower end of the cylinder part 209 a. In this embodiment, thebottom 209 b is formed integrally with the cylinder part 209 a.

In the entire annular region of the upper end face 209 b 1 of the bottom209 b or a part thereof, a region in which a plurality of hydrodynamicgroove are spirally (the spiral direction is opposite to that in FIG. 5)arranged as a portion for producing thrust hydrodynamic pressure, forexample, as in FIG. 5, is formed. This region in which the hydrodynamicgrooves are formed faces the lower end face 222 b of the flange portion222 as a thrust bearing face. While the shaft member 202 is in rotation,the region forms the thrust bearing gap of a second thrust bearingportion T22 described later between itself and the lower end face 222 b(refer to FIG. 19).

The inner periphery face of the housing portion 209 is mainlyconstituted of a large diameter face 209 c where the sleeve portion 208is fixed, a small diameter face 209 d which is provided at the lower endof the large diameter face 209 c and has a diameter smaller than that ofthe large diameter face 209 c. In this embodiment, the upper end face209 e is formed on the shoulder between the large diameter face 209 cand small diameter face 209 d. In the state that the lower end face 208b of the sleeve portion 208 is in contact with the upper end face 209 e,the width in the axial direction from the lower end face 208 b of thesleeve portion 208 to the upper end face 209 b 1 of the bottom 209 b isset to be equal to the axial dimension of the small diameter face 209 d.Accordingly, (the sum of) the thrust bearing gap described later can beobtained highly accurately by controlling the axial dimension of thesmall diameter face 209 d highly accurately.

A sealing portion 210 as a sealing means is formed, for example, of ametallic material or a resin material separately from the housingportion 209, and is fixed by press fitting, adhesion, deposition,welding or other means on the inner periphery of the upper end portionof the cylinder part 209 a of the housing portion 209. In thisembodiment, fixing of the sealing portion 210 is conducted with thelower end face 210 b of the sealing portion 210 in contact the upper endface 208 d of the sleeve portion 208 (for example, refer to FIG. 19).

A tapered face is formed on the inner periphery face 210 a of thesealing portion 210. Between this tapered face and the outercircumferential surface of the shaft portion 221 facing the taperedface, an annular sealing space S2 whose radial dimension upwardly andgradually increases is formed. A lubricating oil is placed in the innerspace of the housing portion 209 sealed by the sealing portion 210, andthe inside of the housing portion 209 is filled with the lubricating oil(dotted region in FIG. 19). In this state, the oil level of thelubricating oil is maintained within the range of the sealing space S2.

As shown in FIG. 17, the shaft member 202 is formed of a metallicmaterial such as stainless steel, and has a T-shaped cross sectionintegrally comprising the shaft portion 221 and the flange portion 222provided at the lower end of the shaft portion 221. On the outerperiphery of the shaft portion 221, radial bearing faces 223 a, 223 bfacing regions on the inner periphery face 208 a of the sleeve portion208 where upper and lower hydrodynamic grooves are formed, respectively,are formed at two axially separated positions.

A concave 225 is formed on the tip face 224 a of the tip portion 224. Inthis embodiment, the concave 225 consists a plastically processedsurface 225 a, and is so configured that its diameter graduallydecreases from the tip face 224 a side toward the center of the shaftportion 221. A cylindrical outer circumferential surface 224 b isprovided at the tip portion 224 of the shaft portion 221 positioned onthe opposite side in the axial direction of the flange portion 222, anda hub 203 is fixed on this outer circumferential surface 224 b by pressfitting, adhesion or other means. Note that annular recess portions 226,227, 228 are formed between the two radial bearing faces 223 a, 223 b,between the lower radial bearing face 223 b and the flange portion 222,and between the upper radial bearing face 223 a and outercircumferential surface 224 b, respectively.

In the fluid lubrication bearing apparatus 201 having the aboveconstitution, while the shaft member 202 is in rotation, a hydrodynamicgroove formation region formed on the inner periphery face 208 a of thesleeve portion 208 forms a radial bearing gap between itself and theradial bearing faces 223 a, 223 b of the shaft portion 221 facing it. Inaddition, as the shaft member 202 rotates, the lubricating oil in theabove radial bearing gap is pushed to the axial center side of thehydrodynamic groove (refer to FIG. 4), and its pressure is increased. Asmentioned above, a first radial bearing portion R21 and a second radialbearing portion R22 which support the shaft portion 221 in a non-contactmanner in the radial direction are constituted, respectively, by thehydrodynamic effect of the lubricating oil produced by the hydrodynamicgrooves.

Simultaneously, the pressure of the lubricating oil film formed in thethrust bearing gap between the lower end face 208 b of the sleeveportion 208 (hydrodynamic groove formation region) and the upper endface 222 a of the flange portion 222 facing it, and the pressure in thethrust bearing gap between a region formed on the upper end face 209 b 1of the bottom of the housing portion 209 where the hydrodynamic groovesare formed and the lower end face 222 b of the flange portion 222 facingit are increased by the hydrodynamic effect of the hydrodynamic grooves.In addition, a first thrust bearing portion T21 and a second thrustbearing portion T22 which support the flange portion 222 (shaft member202) in the thrust direction in a non-contact manner are constituted bythe pressure of these oil films, respectively.

The production method of the shaft member 202 constituting the abovefluid lubrication bearing apparatus 201 will be described below.

The shaft member 202 is produced mainly in the following two steps: aforming step (E), and a grinding step (F). In this procedure, the (E)forming step comprises a shaft material forging process (E-1) and ashaft portion correcting process (E-2). Moreover, the (F) grinding stepcomprises a width grinding process (F-1), a full face grinding process(F-2), and finish grinding process (F-3). In this embodiment, the (E-1)shaft material forging process is mainly described.

(E) Forming Step

(E-1) Shaft Material Forging Process

To begin with, a material of the shaft member 202 to be formed, i.e., abar material made of metal such as stainless steel is compression-formed(forging process) by using molds, for example, in a cold state, so that,for example, the shaft material 212 integrally having the regioncorresponding to the shaft portion (hereinafter referred to simply as ashaft portion) 213 and the region corresponding to the flange portion(hereinafter referred to simply as a flange portion.) 214 is formed{shaft material forging process (E-1)} as shown in FIG. 20.

As mentioned above, if the shaft material 212 is formed by forging, nocutting powders are produced by processing, wasted of the material canbe reduced, and a cleaning step after the process can also besimplified. Moreover, since it is a pressing operation, the cycle timeper one piece of the shaft material 212 can be shortened, improving theproductivity.

Methods which can be employed as the above forging process includeextrusion, upsetting process and other various processes, and aprocessing method suitable for the shape of the processed article isselected. For example, in the shaft material 212 in the shape shown inFIG. 20, to increase the forming accuracy of the shaft portion 213, forexample, it is possible to employ a method comprising roughly formingthe shaft material 212 from a wire by a different forging, and thencompressing the shaft material 212 by mold clamping with molds 216, 217in the axial direction to cause the shaft portion 213 to overhang in theradial direction, as shown in FIG. 21.

In this case, although sufficient compressive force can be applied tothe portions in the vicinity of the dividing face of the molds 216, 217such as the flange portion 214 and the end on the flange portion 214side of the shaft portion 213, compressive force is not sufficientlytransmitted to the portions which are far from the dividing face such asthe tip portion 215 of the shaft portion 213 on the side opposite to theflange portion 214. Consequently, deformation in the radial directionassociated with compression becomes insufficient in particular at thetip portion 215. For example, as shown in FIG. 22, the closer to the tipface 215 a, the tip portion 215 of the shaft portion 213 tends to betapered.

In contrast, for example, if a protrusion 218 of the shape shown in FIG.23 is provided at the center portion of a formed surface 217 acorresponding to the tip face 215 a of the mold 217, a concave 225having the shape corresponding to the protrusion 218 a is formed on thetip face 215 a of the tip of the shaft portion 215. Since this concave225 is formed by pushing the protrusion 218 into the tip face 215 a tocause the corresponding region to undergo plastic deformation, the tipportion 215 is caused to overhang by such plastic deformation, wherebythe shortage of plastic deformation at the tip portion 215 can becompensated. In this embodiment, plastic flow in the outer radialdirection occurs uniformly in the axial direction and the outercircumferential surface 215 b overhang to the shape corresponding to theinner periphery face 217 a of the mold 217, whereby tapering of the tipportion 215 can be prevented and the tip portion 215 having a constantdiameter can be formed.

Note that in the example shown in FIG. 23, described is the case wherethe concave 225 is formed on the tip face 215 a so that the tip portion215 is caused to overhang and the tip portion 215 is deformed until theshape in which the diameter of the outer circumferential surface 215 bbecomes constant (i.e., an intermediate shape) is reached, but it is notnecessarily be caused to overhang to such a degree. For example, theshape of the concave 225 (protrusion 218) and its size can be set in agrinding step described later so that the tip portion 215 is caused tooverhang until the final finished shape is reached. In this embodiment,the final finished shape of the tip portion 224 of the shaft member 202as a finished product is defined by the outer circumferential surface224 b of the tip portion 224, tip face 224 a and a chamfer 224C providedbetween the faces 224 a, 224 b. Therefore, in this case, the followinggrinding step is enabled by causing it to overhang somewhat larger thanthe shape defined by the faces 224 a, 224 b, 224C, obtaining the shaftmember 202 having high dimensional accuracy.

Moreover, in this embodiment, since the concave 225 is in such a shapethat its diameter gradually decreases from the tip face 224 a side tocenter of the shaft portion 221, the closer to the tip face 215 a sidein plastic processing of the concave 225, the greater the amount ofdeformation in the outer radial direction. Therefore, tapering of thetip portion 215 can be prevented and the shaft portion 213 can be formedmore accurately by forming the concave 225 in such a shape.

The forming/forging step can be performed, as mentioned above,separately in two or more forging steps, or for example, a wire havingconstant diameter can be formed in one forging step. Moreover, in thisembodiment, the case where forming of the shaft material 212 and formingof the concave 225 are performed with a common mold is described, butforming of both is not necessarily performed simultaneously. Forexample, after forming the shaft material 212 by forging, the sameaction as that mentioned above can be obtained as above by forming theconcave 225 by forging.

(E-2) Correcting Process

To increase the dimensional accuracy of the shaft material 212 formed bya forging process, in particular the cylindricity of the facecorresponding to the outer circumferential surface 213 a of the shaftportion of the shaft member 2 as a finished product (hereinafterreferred to simply as the outer circumferential surface of the shaftportion), a plastic processing for correcting the cylindricity isperformed on the outer circumferential surface 213 a of the shaftportion of the shaft material 212 after being subjected to the forgingprocess. Accordingly, the outer circumferential surface 213 a of theshaft portion of the shaft material 212 is corrected, and thecylindricity of the face 213 subjected to the correcting process isimproved to be in a desired range (for example, 10 μm or lower). Whenthe outer circumferential surface 215 b of the tip portion 215 is formedto have the same diameter as the outer circumferential surface 213 a ofthe shaft portion, the outer circumferential surface 215 b is alsosubjected to a correcting process, and the cylindricity of the outercircumferential surface 215 b is improved similarly.

(F) Grinding Step

(F-1) Width Grinding

Both end faces of the shaft material 212 which has been subjected to thecorrecting process, i.e., the tip face 215 a of the shaft portion andthe end face 214 b of the flange portion 214 on the side opposite to theshaft portion (refer to FIG. 20) is ground relative to the outermostdiameter surface 217 subjected to said correcting process of the outercircumferential surface 213 a of the shaft portion (The first grindingstep). A grinding apparatus used in this grinding step is, for example,similar to the grinding apparatus 40 shown in FIGS. 7 and 8. Since otherconstitutions, arrangements and processing manners are based on thefirst embodiment, their explanations will be omitted.

By such a grinding step, the tip face 215 a of the shaft portion and theend face 214 b of the flange portion 214 on the side opposite to theshaft portion are ground. At this time, because the corrected face 213 aof the shaft material 212 is supported by the carrier 41 and thiscorrected face 213 a have high cylindricity, if the perpendicularity ofthe rotation axis of the grind stone 42 and the grinding surface of thegrind stone 42, and the parallelism of the rotation axis of the grindstone 42 and the rotation axis of the carrier 41, etc. are highlyaccurately controlled in advance, said both end faces 215 a, 214 b ofthe shaft material 212 can be highly accurately finished relative tothis corrected face 213 a, and the value of the perpendicularityrelative to the corrected face 213 a can be suppressed to a low level.Moreover, the axial width of the shaft material 212 (the entire lengthincluding the flange portion 214) is finished to have a predeterminedsize.

(F-2) Full Face Grinding Process

Subsequently, the outer circumferential surface 213 a and the end face214 a of the flange portion 214 on the shaft portion side of the shaftmaterial 212 relative to both end faces 215 a, 214 b of the ground shaftmaterial 212 are ground (second grinding step). The grinding apparatusused in this grinding step is, for example, similar to the grindingapparatus 50 shown in FIG. 9.

Moreover, a grind stone used in this grinding is a formed grind stonecomprising a grinding surface corresponding to the outer circumferentialsurface shape of the shaft member 202 as a finished product, and,although not shown in the Figs., comprises radial bearing faces 223 a,223 b; outer circumferential surface 224 b of the tip portion; a chamfer224 c; recess portions 226-228, outer circumferential surface 222 c ofthe flange portion 222; and a grinding surface which grinds a regioncorresponding to upper end face 222 a of the flange portion 222. Sinceother constitutions, arrangements and processing manners are based onthe first embodiment, their explanations are omitted.

By such a grinding process, out of the outer circumferential surface ofthe shaft portion 221 of the shaft member 202, the radial bearing faces223 a, 223 b and the outer circumferential surface 224 b of the tipportion, and the region corresponding to the chamfer 224C are ground,and the outer circumferential surface 222C of the flange portion 222 andthe recess portions 226-228, the upper end face 222 a of the flangeportion 222 are further formed. In this grinding step, since theaccuracy setting of the perpendicularity of both end faces 215 a, 214 bof the shaft material 212 (both end faces 224 a, 222 b of the shaftmember 202) has been conducted previously in the width grinding, each ofthe to-be-ground surfaces can be ground highly accurately.

(F-3) Finish Grinding Process

Among the faces which have been ground in full face grinding process,the radial bearing faces 223 a, 223 b of the shaft member 202, and theregion corresponding to the outer circumferential surface 224 b of thetip portion are subjected to the final finish grinding process. Agrinding apparatus used in this grinding is, for example, similar to thegrinding apparatus 60 shown in FIG. 10. Since other constitutions,arrangements and processing manners are based on the first embodiment,their explanations will be omitted.

By such a grinding process, the radial bearing faces 223 a, 223 b andthe region corresponding to the outer circumferential surface 224 b ofthe tip portion are ground, and these regions are finished to have thefinal surface accuracy.

After the above (E) forming step and (F) grinding step, heat treatmentand cleaning process, if necessary, are performed to complete the shaftmember 202 shown in FIG. 17.

The shaft member 202, as long as it is produced by the production methodmentioned above, can be formed so that the shaft portion 221, inparticular the tip portion 224 of the shaft portion 221 is caused tooverhang until at least a final finished shape is reached, and saidouter circumferential surface 215 b can be finished highly accurately bythe following grinding. Accordingly, a fixing area between the hub 203and said outer circumferential surface 215 b can be ensured to obtainhigh fixing strength and fixing accuracy between the hub 203 and theouter circumferential surface 215 b. Moreover, according to such aconstitution, it is possible to readily deal with the elongation of theshaft member 202 by adjusting the size of the concave 225 formed on thetip face 224 a of the shaft portion or the like.

In the above embodiment (first embodiment), the case where the radialbearing faces 23 a, 23 b of the shaft member 2 and thrust bearing faces22 a, 22 b are all smooth surface having no hydrodynamic grooves wasexemplified, but hydrodynamic grooves may be formed on these bearingfaces. In this case, the radial hydrodynamic groove can be formed byrolling or forging, and the thrust hydrodynamic grooves can be formed bypressing or forging at the stage preceding the full face grindingprocess shown in FIG. 8. Similarly, hydrodynamic grooves can be alsoformed on the shaft member 102 according to the second embodiment andthe shaft member 202 according to third embodiment.

Moreover, in the embodiments described above, as the hydrodynamicbearing constituting the radial bearing portions R1, R2 and the thrustbearing portions T1, T2, for example, bearings using hydrodynamicpressure producing parts comprising hydrodynamic grooves arranged in aherringbone shape and a spiral shape are shown as examples, but theconstitution of the hydrodynamic pressure producing parts are notlimited to these. Examples of the radial bearing portions R1, R2 usedinclude a multirobe bearing, step bearing, taper bearing, taper flatbearing or the like. Examples of the thrust bearing portions T1, T2 usedinclude a step pocket bearing, tapered pocket bearing, tapered flatbearing or the like. Hydrodynamic bearings having similar constitutionscan be used for the radial bearing portions R11, R12 and the thrustbearing portions T11, T12 according to the second embodiment and theradial bearing portions R21, R22 and thrust bearing portions T21, T22according to the third embodiment.

Moreover, as for the second and third embodiments, the radial bearingportions R11, R12 and thrust bearing portions T11, T12 can be alsoconstituted of bearings other than hydrodynamic bearings, for example, apivot bearing can be used as the thrust bearing portion, and acylindrical bearing as a radial bearing portion.

Moreover, in the embodiments described above, a lubricating oil ismentioned as an example of a fluid which fills the inside of thehydrodynamic bearing apparatus 1, and produces hydrodynamic effect inthe radial bearing gap between the bearing sleeve 8 and the shaft member2 and in the thrust bearing gaps W1, W2 between the bearing sleeve 8 andhousing 7 and the shaft member 2. However, such a fluid is notparticularly limited to this fluid. As a fluid which can producehydrodynamic effect in the bearing gaps having hydrodynamic grooves, forexample, a gas such as air and a lubricant having fluidity such as amagnetic fluid may be used. Of course, similar kind of fluids may beused for the fluid lubrication bearing apparatus 101, 201 according tothe second and third embodiments.

The fluid lubrication bearing apparatus according to the presentinvention is suitable for information appliances, for example, Magneticdisk apparatuses such as HDD, optical disk apparatuses such as CD-ROM,CD-R/RW and DVD-ROM/RAM, spindle motors for magneto-optic diskapparatuses such as MD and MO, polygon scanner motors of laser beamprinters (LBP), color wheel motors of projectors, or small motors suchas fan motors.

1. A method of producing a metallic shaft member for a fluid lubricationbearing apparatus, the metallic shaft member integrally including ashaft portion and a flange portion provided on an end of the shaftportion, the method comprising: forming the shaft portion with a forgingprocess including compressing a shaft material integrally having aregion corresponding to the shaft portion and a region corresponding tothe flange portion provided on an end of the region corresponding to theshaft portion in an axial direction of the shaft material by moldclamping a set of molds having a constant diameter that is larger thanan initial constant diameter of the region of the shaft materialcorresponding to the shaft portion such that the region corresponding tothe shaft portion deforms with an increase in diameter; and forming aconcave at a tip face of a tip portion of the region corresponding tothe shaft portion by applying compression force to the regioncorresponding to the flange portion by mold clamping the set of moldsand pushing the shaft material against a protrusion at a bottom of amold of the set of molds, during the forming of the shaft portion withthe forging process, such that the tip portion deforms with an increasein diameter by a plastic flow with the forming of the concave, an amountof deformation of the tip portion being uniform in the axial direction.2. A method of producing a shaft member according to claim 1, whereinthe forming of the concave comprises pushing the shaft material againstthe protrusion, during the forming of the shaft portion with the forgingprocess, such that the tip portion deforms with the increase in diameteruntil the tip portion reaches a final finished shape or an intermediateshape.
 3. A method of producing a shaft member according to claim 2,further comprising processing the tip portion of the shaft portionhaving the intermediate shape by grinding after the forging process toachieve the final finished shape defined by an outer circumferentialsurface of a tip of the shaft portion, the tip face of the shaft portionand a chamfer between the outer circumferential surface and the tipface.